Respiratory System

Question 1

Respiration definition

Answer 1

gas movement & gas metabolism

Question 2

Internal respiration definition

Answer 2

intra- cellular metabolic processes (in mitochondria) that use O2 & produce CO2
– “cellular respiration”

Question 3

External respiration definition

Answer 3

events involved in exchange of O2 & CO2 between cells & external environment

Question 4

4 steps of external respiration

Answer 4

1- Ventilation (breathing)
2- Respiratory exchange (at lungs or gills)
3- Circulation
4- Cellular exchange (between blood & cells)

Question 5

What is gas exchange governed by?

Answer 5

partial pressure
(Molecules diffuse down concentration gradients
But gases diffuse down partial pressure gradients)

Question 6

Partial pressure (PP or P)

Answer 6

pressure exerted by a particular gas within a mixture of gases
measured in mm Hg

Question 7

Total atmospheric pressure

Answer 7

sum of partial pressures that each gas in atmosphere contributes
Pressure exerted on objects by atmospheric air can push a column of mercury (Hg) up some amount of mm = total atmospheric pressure
Atmospheric air contains N2 (~79%), O2 (~21%), plus small amounts of CO2, H2O vapor, other gases, & pollutants

Question 8

Calculating partial pressures

Answer 8

Total atmospheric pressure at sea level = 760 mm Hg
21% of that = O2 so PO2 = 160 mm Hg

At elevation, total atmospheric pressure drops = partial pressure of all gases drops = less drive for O2 diffusion into tissues

Question 9

strategies for increasing gas exchange:

Answer 9

Diffusion is slow except over short distances

1. To maximize gas exchange, epithelial lining of respiratory surface (e.g. lungs) must be very thinAlso want as much surface area as possible for as much diffusion as possible to take place
2. To increase surface area, respiratory surfaces in vertebrates have specialized folds: invaginations (in-pockets) & evaginations (out-pockets)
   Steeper partial pressure gradient = faster diffusion
3. Respiratory pigments (e.g. hemoglobin in erythrocytes) bind O2, which means it is no longer freely dissolved & no longer contributing to partial pressure inside the body

Maintains low PO2 inside body, keeping gradient steep & allowing for greater diffusion, plus prevents any backwards diffusion

Question 10

Respiratory anatomy

Answer 10

In vertebrates, water respirers have gills while air respirers have lungs
Each is adapted to specialized needs
Less O2 in water
Potential for desiccation in air

Question 11

Gills

Answer 11

have many evaginations & very thin epithelial cells to increase gas exchange

1 other adaptation: countercurrent blood flow

Blood flows counter to water across gills – causes PP gradient all along gills rather than reaching equilibrium & O2 diffusion stopping

Question 12

lungs

Answer 12

Dry air can cause desiccation (& death) of sensitive epithelial cells in the lungs

Lungs must stay moist & lubricated for protection & easy movement during inhalation & exhalation

Mucus-secreting cells produce an aqueous mucus lubricant: “pulmonary surfactant”

Ciliated cells are lined with tiny hairs that help distribute the mucus

Question 13

Mammals have a very high metabolic rate affect on lungs

Answer 13

had to significantly increase lung surface area

Accomplished this with numerous small alveoli covered by incredibly dense capillaries

Alveoli = small sacs in grape-like clusters where gas exchange in lungs takes place

~300 million in a human!

Question 14

Anatomy of mammalian lungs

Answer 14

Nasal passages  pharynx (throat)  trachea  right & left bronchi  bronchioles  alveoli
The trachea & larger bronchi must be open most or all of the time, so are rigid structures with cartilaginous rings to prevent compression

Smaller bronchioles do not have cartilage – instead have smooth muscle with autonomic innervation & sensitivity to hormones

thus can have altered contraction to regulate amount of air flow

Question 15

Alveoli

Answer 15

have no cartilage or smooth muscle to help them inflate & deflate

Instead rely on on muscles in the thoracic (chest) cavity: diaphragm, external intercostal, abdominal wall, & internal intercostal muscles

these change the volume of the thoracic cavity, causing a corresponding change in lung volume

Question 16

Mammalian lungs

Answer 16

take up most of the thoracic cavity

Each lung is enclosed within the double- walled pleural sac

inside of sac is filled with fluid allowing the layers to slide past each other during respiratory movement

The inside of the pleural sac (where the lungs are) = pleural cavity

Question 17

Inspiration (inhalation)

Answer 17

breath in
When relaxed, the diaphragm muscle is in a dome shape, protruding into thoracic cavity
Upon contraction, diaphragm moves downward, thereby enlarging area in thoracic cavity & causing inward air flow
Contraction of the external intercostal muscles also enlarges the thoracic cavity by expanding ribs & sternum outward, allowing inward air flow

Question 18

Passive expiration (exhalation) = breath out

Answer 18

As inspiratory muscles relax back into thoracic cavity & lungs exhibit elastic recoil, air is passively pushed out of lungs, with gases diffusing down their PP gradients

Question 19

While expiration occurs passively during quiet breathing, it is possible to actively push air out too

Answer 19

moves air out more completely & rapidly, especially useful for quick breathing during exercise

when contracted, abdominal wall muscles push the diaphragm even further into the thoracic cavity

Question 20

Internal intercostal muscles

Answer 20

have opposite effect of external intercostal muscles, causing ribs to flatten

Question 21

Airways normally offer very little resistance

Answer 21

Allows adequate air flow even when pressure gradients are very small (1 or 2 mm Hg)

Various respiratory diseases can narrow airways, increasing resistance & thus decreasing airflow

e.g. COPD = chronic obstructive pulmonary disease, a group of lung diseases including chronic emphysema, bronchitis, & asthma

Question 22

Lung volumes can be measured by:

Answer 22

a spirometer

fits over mouth & measures volume of air breathed in & out  generates a spirogram

this shows the various volumes & capacities of the lungs

Question 23

Total lung capacity (TLC)

Answer 23

the maximum amount of air lungs can hold

~5.7L in humans, though affected by build, age, lung health, & disease

However, not all of TLC can be exchanged

Question 24

residual volume(RV)

Answer 24

air that cannot be expelled

Question 25

Tidal volume (TV)

Answer 25

amount of air moving into or out of the lungs during any one breathing cycle At rest, human TV = ~2.2L at end of expiration to ~2.7L at end of inspiration

Question 26

Functional residual capacity (FRC)

Answer 26

volume of air left in lungs after passive expiration – during quiet breathing, lungs are not close to max expiration or inspiration

Question 27

inspiratory reserve volume (IRV)

Answer 27

After normal inspiration it is possible to breathe in additional air

Question 28

expiratory reserve volume (ERV)

Answer 28

After normal expiration it is possible to exhale additional air from the lungs

Question 29

vital capacity (VC):

Answer 29

3 values (TV, IRV, & ERV) added represent it amount of air we can control through inhalation & exhalation usually ~3-5L in vol.

Question 30

Pulmonary ventilation

Answer 30

the volume of air breathed in & out in 1 minute PV= TV x Respiratory Rate Increasing TV or rate increases pulm. ventilation However: more advantageous to increase TV rather than rate because of anatomic dead space – the area where air is not available for gas exchange at alveoli (can’t get past conducting airways like bronchi) Thus a better measure of gas exchange = alveolar ventilation, where dead space is accounted for

Question 31

Obstructive lung disease

Answer 31

any problem that doesn’t allow air to move smoothly from alveoli out through trachea (or vice versa) when breathing e.g. COPD, & smoking cigarettes also permanently damages alveoli, leading to lung obstruction Spirometry data can be helpful in diagnosing obstructive & restrictive lung diseases

Question 32

Restrictive lung disease

Answer 32

normal airflow but decreased lung volumes e.g. due to pulmonary fibrosis, asbestos poisoning, respiratory distress syndrome, & pneumonia obesity can also cause decreased lung volumes because of increased pressure on the chest wall

Question 33

forced expired volume in one second (FEV1)

Answer 33

FEV1 = the volume expired in the first second of maximal expiration after a full inspiration – is a measure of how quickly the lungs can be emptied In healthy adults the FEV1/FVC ratio = ~80% Decreased by obstructive lung disease, damage, or naturally with age (~70% or less)

Question 34

Oxygen is dissolved in blood:

Answer 34

as free gas, though very little because O2 is poorly soluble in warm fluids (only 1-5%) bound to respiratory pigments in erythrocytes, like hemoglobin

Question 35

The vast majority of O2 in blood is carried in circulation by:

Answer 35

hemoglobin ensures enough O2 gets to tissues also remember: bound O2 doesn’t contribute to PP, so helps keep PP gradient steep

Question 36

hemoglobin (Hb)

Answer 36

Main respiratory pigment in vertebrates Hemoglobin contains iron (Fe) molecules & forms a loose, easily reversible combo between Fe & O2 Hb unbound = deoxyhemoglobin, or “reduced” HbO2 = oxyhemoglobin

Question 37

So why does Hb combine with O2 in the lungs but release O2 at the tissues?

Answer 37

1st: Hb & O2 binding increases when the PP of O2 is high &decreases when low 2nd: HbO2 tends to dissociate under several conditions that occur at tissues (but not lungs) & are especially increased at tissues working hard Increased PCO2 Increased acidity (e.g. lactic acid) Increased temp Increased free phosphates inside erythrocytes (affects lungs too – produced during RBC metabolism)

Question 38

So how is CO2 transported in the blood?

Answer 38

1- As freely dissolved gas CO2 more soluble than O2, but still only ~5-10% of CO2 in blood is dissolved 2- Bound to hemoglobin ~25% of CO2 in blood is carried bound to Hb (HbCO2) only in mammals – fish have altered Hb which can’t bind CO2 3- As bicarbonate (HCO3-) CO2 is converted into HCO3

Question 39

HCO3- is the most important means of CO2 transport because

Answer 39

HCO3- is more soluble in the blood than CO2 – thus easier to transport than free gas HCO3- cannot diffuse through membranes on its own – thus more controllable than free gas

Question 40

HCO3- / Cl- antiport carrier passively facilitates diffusion across erythrocyte membrane

Answer 40

Allows plasma to “soak up” CO2, preventing buildup in RBCs exchange with Cl- (“chloride shift”) prevents change in electrical gradient across membrane

Question 41

Back at lungs, transport moves in opposite direction

Answer 41

Causes restoration of Cl- gradients HCO3- reaction takes place in reverse to allow release of CO2 from blood to lungs as free gas

Question 42

We’ve now seen that Hb can bind to O2, CO2, & H+ - so how does it choose which one & where?

Answer 42

Remember: high PO2 at lungs encourages binding (HbO2), & conditions at tissues (low O2, high CO2, high acidity, etc.) encourage dissociation As HbO2 unbinds, the affinity of Hb for CO2 & H+ increases  called the “Haldene effect” Results in HbH+ & HbCO2 Dissociate at lungs & cycle starts again

Question 43

Carbon monoxide (CO)

Answer 43

can also bind to Hb CO2, O2, & H+ all readily dissociate from Hb CO binds to Hb preferentially (more than O2) & does NOT readily dissociate not enough O2 to tissues, CO poisoning

Question 44

Hypoxia

Answer 44

insufficient O2

Question 45

Hypercapnia

Answer 45

excess CO2 in blood caused by excess CO2 in environment or hypoventilation Hypercapnia-->  elevated carbonic acid production-->  excess H+ --> respiratory acidosis

Question 46

Hypocapnia

Answer 46

low CO2 in blood caused by hyperventilation Hypocapnia --> drop in carbonic acid production-->  less H+ than usual --> respiratory alkalosis

Question 47

Why are changes in CO2 dangerous?

Answer 47

Changes in blood CO2 affect acid-base balance CO2 + H2O  H2CO3  H+ + HCO3- Remember the importance of homeostasis, including of pH: low (acidic) or high (basic) pH = denaturation of proteins & irreversible cell damage

Question 48

bronchodilation

Answer 48

Sympathetic stimulation | during exercise or other times when O2 needs increase

Question 49

bronchoconstriction

Answer 49

Parasympathetic stimulation | when quiet & relaxed

Question 50

Like arterioles, the smooth muscle on bronchioles is sensitive to local CO2 levels

Answer 50

High CO2 levels act directly on the smooth muscle, causing relaxation / dilation, while low CO2 levels cause contraction / constriction

Question 51

Like blood flow, air flow is detected by peripheral chemoreceptors in the aorta & carotid artery

Answer 51

Chemoreceptors detect low O2, high CO2, & high H+ send info to respiratory center of the brain (in medulla) However, these are only weakly stimulated – main regulators of ventilation are central chemoreceptors

Question 52

Central chemoreceptors (in the brain) detect CO2 (weakly) & H+ (strongly), sending signals to the respiratory center to adjust ventilation

Answer 52

H+ cannot cross BBB on its own, but is produced in the brain when the bicarbonate reaction takes place